Homologous as well as heterologous unfertilized oocytes were fused with a high rate of success utilizing polyethylene glycol. Ultrastructural studies showed that oocyte fusion products have undergone normal cortical reaction and completed second meiotic division. Roughly one-third of the OFPs developed into blastocysts. Chimeras of 2-cell OFPs and 2-cell stages from genetically different mice developed at a high rate into blastocysts. Future studies will focus on utilizing an electrical cell fusion system and reciprocal nuclear transfers between OFPs and fertilized eggs of a genetically different strain of mice.